U.S. patent application number 10/701499 was filed with the patent office on 2004-12-02 for heat spreader and semiconductor device and package using the same.
This patent application is currently assigned to Kabushik Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Hayashi, Kazushi, Inoue, Kenichi, Kawakami, Nobuyuki, Kobashi, Koji, Kobori, Takashi, Tachibana, Takeshi, Yokoto, Yoshihiro.
Application Number | 20040238946 10/701499 |
Document ID | / |
Family ID | 33455395 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040238946 |
Kind Code |
A1 |
Tachibana, Takeshi ; et
al. |
December 2, 2004 |
Heat spreader and semiconductor device and package using the
same
Abstract
A semiconductor device and package has a heat spreader directly
disposed on the reverse surface of the semiconductor device. This
heat spreader includes a diamond layer or a layer containing
diamond and ceramics such as silicon carbide and aluminum nitride.
The heat spreader is directly formed on a substrate for the
semiconductor device. In particular, the heat spreader is composed
of a diamond layer and one or two metal or ceramic members, which
are bonded to the diamond layer with one or two polymer adhesive
layers. This diamond layer has a fiber structure across the
thickness or a microcrystalline structure. Cilia are formed on a
surface of the diamond layer facing the one or two metal or ceramic
members.
Inventors: |
Tachibana, Takeshi;
(Kobe-shi, JP) ; Hayashi, Kazushi; (Kobe-shi,
JP) ; Inoue, Kenichi; (Kobe-shi, JP) ; Yokoto,
Yoshihiro; (Kobe-shi, JP) ; Kobashi, Koji;
(Kobe-shi, JP) ; Kawakami, Nobuyuki; (Kobe-shi,
JP) ; Kobori, Takashi; (Kobe-shi, JP) |
Correspondence
Address: |
Reed Smith, LLP
Suite 1400
3110 Fairview Park Drive
Falls Church
VA
20042
US
|
Assignee: |
Kabushik Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
|
Family ID: |
33455395 |
Appl. No.: |
10/701499 |
Filed: |
November 6, 2003 |
Current U.S.
Class: |
257/706 ;
257/E23.111 |
Current CPC
Class: |
H01L 2924/12044
20130101; H01L 2924/0002 20130101; H01L 2924/0002 20130101; H01L
23/3732 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/706 |
International
Class: |
H01L 023/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2002 |
JP |
2002-324543 |
Nov 7, 2002 |
JP |
2002-324473 |
Claims
1. A semiconductor device having a heat spreader comprising diamond
or a diamond-containing material having a thermal conductivity of
350 W/(m.multidot.K) or more, the heat spreader being directly
disposed entirely or partially on the reverse surface of the
semiconductor device.
2. The semiconductor device according to claim 1, wherein the
diamond-containing material is a composite of a diamond layer and a
ceramic layer or a mixture of diamond particles and ceramic
particles, the ceramic layer or the ceramic particles comprising at
least one of silicon carbide and aluminum nitride.
3. The semiconductor device according to claim 1, wherein the heat
spreader is directly disposed on a substrate for the semiconductor
device.
4. The semiconductor device according to claim 1, wherein the heat
spreader has an irregular surface facing away from the
semiconductor device.
5. A semiconductor package accommodating the semiconductor device
having a heat spreader comprising diamond or a diamond-containing
material having a thermal conductivity of 350 W/(m.multidot.K) or
more, the heat spreader being directly disposed entirely or
partially on the reverse surface of the semiconductor device,
wherein a metal heat sink or a metal radiating fin is bonded on a
surface of the heat spreader facing away from the semiconductor
device.
6. The semiconductor package according to claim 5, wherein a
polymer adhesive layer is used to bond the metal heat sink or the
metal radiating fin on the surface of the heat spreader, and cilia
are formed on the surface of the heat spreader so that the polymer
adhesive layer spreads over part of the cilia.
7. A heat spreader disposed on a semiconductor device accommodated
in a sealed semiconductor package to dissipate heat from the
semiconductor device, the heat spreader comprising: a diamond layer
having a fiber structure across the thickness; and one or two metal
or ceramic members bonded on one or both surfaces of the diamond
layer.
8. The heat spreader according to claim 7, wherein the one or two
metal or ceramic members are bonded to the diamond layer with one
or two polymer adhesive layers.
9. The heat spreader according to claim 8, wherein cilia are formed
on the one or both surfaces of the diamond layer.
10. The heat spreader according to claim 7, wherein the diamond
layer has a thermal conductivity of 500 W/(m.multidot.K) or more
across the plane and thickness, and the bonding surfaces of the
diamond layer and the one or two metal or ceramic members have a
thermal conductivity of 4.times.10.sup.6 W/(m.sup.2.multidot.K) or
more.
11. The heat spreader according to claim 7, wherein the diamond
layer is formed by chemical vapor deposition and has a thickness of
20 to 100 .mu.m.
12. The heat spreader according to claim 9, wherein the cilia have
lengths of 0.2 to 3 .mu.m.
13. A semiconductor package having the heat spreader disposed on a
semiconductor device accommodated in a sealed semiconductor package
to dissipate heat from the semiconductor device, the heat spreader
comprising: a diamond layer having a fiber structure across the
thickness; and one or two metal or ceramic members bonded on one or
both surfaces of the diamond layer.
14. A heat spreader disposed on a semiconductor device accommodated
in a sealed semiconductor package to dissipate heat from the
semiconductor device, the heat spreader comprising: a diamond layer
having a microcrystalline structure; and one or two metal or
ceramic members bonded on one or both surfaces of the diamond
layer.
15. The heat spreader according to claim 14, wherein the one or two
metal or ceramic members are bonded to the diamond layer with one
or two polymer adhesive layers.
16. The heat spreader according to claim 15, wherein cilia are
formed on the one or both surfaces of the diamond layer.
17. The heat spreader according to claim 14, wherein the diamond
layer has a thermal conductivity of 500 W/(m.multidot.K) or more
across the plane and thickness, and the bonding surfaces of the
diamond layer and the one or two metal or ceramic members have a
thermal conductivity of 4.times.10.sup.6 W/(m.sup.2.multidot.K) or
more.
18. The heat spreader according to claim 14, wherein the diamond
layer is formed by chemical vapor deposition and has a thickness of
20 to 100 .mu.m.
19. The heat spreader according to claim 16, wherein the cilia have
lengths of 0.2 to 3 .mu.m.
20. A semiconductor package having the heat spreader disposed on a
semiconductor device accommodated in a sealed semiconductor package
to dissipate heat from the semiconductor device, the heat spreader
comprising: a diamond layer having a microcrystalline structure;
and one or two metal or ceramic members bonded on one or both
surfaces of the diamond layer
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to heat spreaders for
semiconductor devices to prevent a temperature rise due to heat
generated by the semiconductor devices. In addition, the present
invention relates to semiconductor devices and packages with the
heat spreaders.
[0003] 2. Description of the Related Art
[0004] To facilitate heat dissipation from semiconductor devices,
for example, a semiconductor package with a combination of a high
thermal-conductivity ceramic base material and a resin wiring
substrate such as a printed circuit board has been proposed in
Japanese Unexamined Patent Application Publication No. 10-275879.
This semiconductor package includes a semiconductor device mounted
on the bottom surface of an aluminum nitride heat spreader and a
resin wiring substrate bonded around the semiconductor device. This
resin wiring substrate has a wiring layer wired to a signal wiring
of the semiconductor device. Semiconductor packages of this type
are expected to, for example, meet high power-consumption
semiconductor devices and achieve a low-resistance, high-density
signal wiring and a low-cost package.
[0005] In these semiconductor packages, however, a large
semiconductor device of, for example, 20 mm by 20 mm requires a
large aluminum nitride substrate. When a metal radiating fin is
bonded entirely on the top surface of such a large aluminum nitride
substrate, the aluminum nitride substrate may cause defects such as
cracking during heat cycles due to the difference in thermal
expansion coefficients between the aluminum nitride substrate and
the metal radiating fin.
[0006] Semiconductor packages using high thermal-conductivity
ceramics, such as the above aluminum nitride substrate, or a metal
plate, such as a copper plate, as a heat spreader have been used in
practice as packages for meeting high power-consumption
semiconductor devices. Nevertheless, these semiconductor packages
have difficulty in meeting a further increase in the
power-consumption of the semiconductor devices. In addition, a heat
spreader made of only high thermal-conductivity ceramics decreases
the reliability of bonding of a heat sink or a radiating fin in a
face-down structure, which is supposed to provide a high
heat-dissipation package. On the other hand, a heat spreader made
of, for example, a copper plate decreases the reliability of
mounting of the semiconductor devices.
[0007] FIG. 8 shows a sectional view of an example of known
semiconductor packages with a heat spreader. A semiconductor device
102 is mounted on a heat spreader 101, which is bonded over an
opening of a ceramic package body 103 such that the semiconductor
device 102 is disposed inside the package body 103. A ceramic cover
104 is disposed on the other opening of the package body 103 to
seal the semiconductor device 102 in this package.
[0008] Such a heat spreader has so far been made of, for example, a
composite material of copper and tungsten, aluminum nitride, or
silicon carbide. Japanese Unexamined Patent Application Publication
No. 9-129793 also discloses a heat transfer plate for semiconductor
packages.
[0009] The heat dissipation characteristics of these known heat
spreaders and semiconductor packages using such heat spreaders seem
to have been improved to the limit in terms of the materials used
and their structures. Therefore, further improvement of the heat
dissipation characteristics is difficult. As a result, the
processing speed, output, and degree of integration of
semiconductor devices must be controlled to suppress the
temperature rise of the packages.
SUMMARY OF THE INVENTION
[0010] In order to solve the above problems, an object of the
present invention is to provide a semiconductor device and package
having a heat spreader that has excellent heat dissipation
characteristics; high reliability of mounting of the semiconductor
device and bonding of a heat sink or a radiating fin; and high
suitability for high power-consumption semiconductor devices.
Another object of the present invention is to provide a reliable
heat spreader having excellent heat dissipation characteristics for
cooling high-speed-processing, high-output semiconductor packages;
high thermal conductivity across the plane and thickness;
sufficient strength, flatness, and air-tightness; good adhesiveness
to semiconductor devices and sealing materials for package bodies;
and sufficiently small thermal stress that is generated by changes
in temperature during bonding or during use to result in a peeling
bonding surface or a defective device, and a semiconductor package
using the heat spreader.
[0011] The present invention provides a semiconductor device having
a heat spreader made of diamond or a diamond-containing material
having a thermal conductivity of 350 W/(m.multidot.K) or more. This
heat spreader is directly disposed entirely or partially on the
reverse surface of the semiconductor device.
[0012] The diamond-containing material may be a composite of a
diamond layer and a ceramic layer or a mixture of diamond particles
and ceramic particles. The ceramic layer or the ceramic particles
may be at least one of silicon carbide and aluminum nitride.
[0013] The heat spreader, for example, may have a transparency of
at least 10% to light at wavelengths of 750 nm or less.
[0014] The heat spreader is preferably directly disposed on a
substrate for the semiconductor device.
[0015] The heat spreader may have an irregular surface facing away
from the semiconductor device.
[0016] The present invention further provides a semiconductor
package accommodating the semiconductor device. In this
semiconductor package, a metal heat sink or a metal radiating fin
may be bonded on a surface of the heat spreader facing away from
the semiconductor device.
[0017] In this semiconductor package, the metal heat sink or the
metal radiating fin is preferably bonded on part of the surface of
the heat spreader.
[0018] In the semiconductor package, a polymer adhesive layer may
be used to bond the metal heat sink or the metal radiating fin on
the surface of the heat spreader. In addition, cilia may be formed
on the surface of the heat spreader so that the polymer adhesive
layer spreads over part of the cilia.
[0019] According to the present invention, the heat spreader can
dissipate a large amount of heat and improve the reliability of
mounting of a semiconductor device or module. Furthermore, the
semiconductor package can reliably accommodate, for example, a high
power-consumption, large semiconductor device.
[0020] The present invention further provides a heat spreader
disposed on a semiconductor device accommodated in a sealed
semiconductor package to dissipate heat from the semiconductor
device. This heat spreader is composed of a diamond layer having a
fiber structure across the thickness; and one or two metal or
ceramic members bonded on one or both surfaces of the diamond
layer.
[0021] In this heat spreader, cilia are preferably formed on the
one or both bonding surfaces of the diamond layer. These cilia
preferably have lengths of 0.2 to 3 .mu.m.
[0022] The present invention provides another heat spreader
disposed on a semiconductor device accommodated in a sealed
semiconductor package to dissipate heat from the semiconductor
device. This heat spreader is composed of a diamond layer having a
microcrystalline structure; and one or two metal or ceramic members
bonded on one or both surfaces of the diamond layer.
[0023] In each of these two heat spreaders, the one or two metal or
ceramic members may be bonded to the diamond layer with one or two
polymer adhesive layers.
[0024] In each of these two heat spreaders, the diamond layer
preferably has a thermal conductivity of 500 W/(m.multidot.K) or
more across the plane and thickness, and the bonding surfaces of
the diamond layer and the one or two metal or ceramic members
preferably have a thermal conductivity of 4.times.10.sup.6
W/(m.sup.2.multidot.K) or more. The diamond layer may be formed by,
for example, chemical vapor deposition and may have a thickness of
20 to 100 .mu.m.
[0025] These heat spreaders may be provided for semiconductor
packages.
[0026] As described above, each heat spreader according to the
present invention is composed of a diamond layer, which has an
extremely high thermal conductivity, and one or two metal or
ceramic members, which have a large thermal conductivity.
Therefore, the heat spreaders have a thermal conductivity, across
the thickness, equal to or more than that of a composite material
of copper and tungsten or that of aluminum nitride, both of which
have been used for heat spreaders. In addition, the heat spreaders
have good air-tightness and are not warped or cracked. Furthermore,
the heat spreaders, having a nearly equivalent thermal expansion
coefficient, across the plane, to that of silicon or ceramics such
as alumina, have small thermal stress that is generated by changes
in temperature. The heat spreaders are thus prevented from defects
such as peeling and cracking, which adversely affect semiconductor
devices.
[0027] The present invention, therefore, can provide a reliable
heat spreader having high thermal conductivity across the plane and
thickness; sufficient strength, flatness, and air-tightness; good
adhesiveness to semiconductor devices and sealing materials for
package bodies; and sufficiently small thermal stress that is
generated by changes in temperature during bonding or during use to
result in a peeling bonding surface or a defective device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIGS. 1A and 1B are sectional views of semiconductor devices
with a heat spreader according to a first embodiment of the present
invention;
[0029] FIGS. 2A and 2B are sectional views of semiconductor devices
with a heat spreader according to a second embodiment of the
present invention;
[0030] FIGS. 3A and 3B are sectional views of semiconductor devices
with a heat spreader according to a third embodiment of the present
invention;
[0031] FIGS. 4A and 4B are sectional views of semiconductor devices
with a heat spreader according to a fourth embodiment of the
present invention;
[0032] FIG. 5A is a sectional view of a heat spreader according to
a fifth embodiment of the present invention;
[0033] FIG. 5B is a sectional view of a heat spreader according to
a modification of the fifth embodiment of the present
invention;
[0034] FIG. 6A is a sectional view of a heat spreader according to
a sixth embodiment of the present invention;
[0035] FIG. 6B is a sectional view of a heat spreader according to
a modification of the sixth embodiment of the present
invention;
[0036] FIG. 7A is a sectional view of a heat spreader according to
a seventh embodiment of the present invention;
[0037] FIG. 7B is a sectional view of a heat spreader according to
a modification of the seventh embodiment of the present
invention;
[0038] FIG. 8 is a sectional view of a known semiconductor package
with a heat spreader; and
[0039] FIG. 9 is an electron micrograph showing a surface of a
ciliary diamond layer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Embodiments of the present invention will now be described
with reference to the attached drawings.
[0041] FIG. 1A is a sectional view of a semiconductor device with a
heat spreader according to a first embodiment of the present
invention. A heat spreader 2 is directly disposed on the reverse
surface of a semiconductor device 1. In the present invention,
semiconductor devices include semiconductor modules. This heat
spreader 2 is made of diamond or a diamond-containing material
having a high thermal conductivity of 350 W/(m.multidot.K) or
more.
[0042] Examples of the diamond-containing material include a
composite of a diamond layer and a ceramic layer and a mixture of
diamond particles and ceramic particles. Examples of the ceramics
used for the diamond-containing material include at least one of
silicon carbide and aluminum nitride.
[0043] Diamond has a thermal conductivity of up to 2200
W/(m.multidot.K). When, however, diamond is used for the heat
spreader, the manufacturing cost rises. Therefore, diamond may be
effectively combined with ceramics such as silicon carbide and
aluminum nitride. A material containing diamond and such ceramics
can produce a heat spreader having a thermal conductivity of 350
W/(m.multidot.K) or more. This heat spreader provides an excellent
heat dissipation effect even for next-next-generation central
processing units (CPUs), which will generate heat of 100 W or
more.
[0044] Aluminum nitride has a thermal conductivity of about 200
W/(m.multidot.K), while silicon carbide has a thermal conductivity
of about 270 W/(m.multidot.K). These ceramics have the highest
conductivity next to that of diamond among ceramics. A combination
with diamond, such as a composite including a diamond layer and a
sintered mixture containing diamond particles, can provide a
thermal conductivity of 350 W/(m.multidot.K) or more.
[0045] The type of the semiconductor device 1 is not limited. The
present invention is particularly effective for a high
power-consumption, large semiconductor device with, for example, a
power consumption of 10 W or more and a size of 10 mm by 10 mm or
more.
[0046] FIG. 1B is a sectional view of a modification of this
embodiment. A heat spreader 3 made of diamond or the
diamond-containing material (a combination of diamond and ceramics
such as silicon carbide and aluminum nitride) has fine
irregularities 3a formed on a surface facing away from the
semiconductor device 1.
[0047] These heat spreaders 2 and 3 have excellent chemical
resistance and do not deteriorate either by air cooling or by water
cooling. Therefore, the heat spreaders 2 and 3 do not decrease the
performance of the semiconductor device 1.
[0048] FIG. 2A is a sectional view of a semiconductor device with a
heat spreader according to a second embodiment of the present
invention. A metal heat sink 4 is bonded on the surface of the heat
spreader 2 (made of diamond or the diamond-containing material)
facing away from the semiconductor device 1.
[0049] FIG. 2B also shows the semiconductor device 1 with the heat
spreader 2 (made of diamond or the diamond-containing material). A
metal radiating fin 5 is bonded on the surface of the heat spreader
2 facing away from the semiconductor device 1.
[0050] General metal heat sinks and metal radiating fins have
largely different thermal expansion coefficients from those of
materials for semiconductor devices. On the other hand, the heat
spreader 2, which is made of diamond or the diamond-containing
material, has a nearly equivalent thermal expansion coefficient to
that of the material for the semiconductor device 1. Therefore, the
heat spreader 2 not only functions as a heat transfer layer but
also as a thermal expansion relieving layer to improve the
reliability of mounting of the semiconductor device 1.
[0051] Preferably, the heat spreader 2 is almost the same size as
the semiconductor device 1 and is formed entirely on the
semiconductor device 1. The heat spreader 2 is basically made of a
single substrate having no wiring layer. This heat spreader 2, if
using the metal heat sink 4 or the metal radiating fin 5 as a
ground or having a ground layer, may have a metallized layer or a
through hole. The heat spreader 2, if including a diamond layer or
a diamond-containing material layer, exhibits excellent
transparency to light with wavelengths of 227 nm or more. This heat
spreader 2, therefore, functions as a light-emitting/receiving
window of optical semiconductors while having no through hole to
retain the greatest possible performance as a heat spreader. In
particular, a heat spreader directly disposed on the reverse
surface of a semiconductor device before or during a step of
preparing the semiconductor device, as in the present invention, is
effective for a wide variety of semiconductor modules such as diode
arrays.
[0052] The metal heat sink 4 or the metal radiating fin 5 may be
bonded to the heat spreader 2 by various methods. Examples of
the-methods include brazing with an active metal, bonding of a
metallized heat spreader with solder or general brazing filler
metals, and bonding with general resin adhesives.
[0053] FIGS. 3A and 3B are sectional views of semiconductor devices
with a heat spreader according to a third embodiment of the present
invention. The metal heat sink 4 or the metal radiating fin 5 is
bonded to the heat spreader 2 (made of diamond or the
diamond-containing material) with a metal bonding layer 6. This
metal bonding layer 6 is provided not entirely but partially on the
bonding surfaces of the heat spreader 2 and the metal heat sink 4
or the metal radiating fin 5. The metal bonding layer 6 can reduce
stress caused by the difference in thermal expansion coefficients
between the different materials. Examples of the material for the
metal bonding layer 6 include gold, silver, copper, aluminum, and
their alloys.
[0054] FIGS. 4A and 4B are sectional views of semiconductor devices
with a heat spreader according to a fourth embodiment of the
present invention. The metal heat sink 4 or the metal radiating fin
5 is bonded to the heat spreader 2 (made of diamond or the
diamond-containing material) with a polymer adhesive layer 7, which
is a polymer adhesive such as thermosetting resin sheets or pastes.
This polymer adhesive layer 7 is provided between the heat spreader
2 and the heat sink 4 or radiating fin 5. If cilia are formed on
the bonding surface of the heat spreader 2, the polymer adhesive
layer 7 spreads over part of these cilia. The cilia are
significantly effective from the viewpoints of adhesion and stress
reduction.
[0055] To form such cilia, for example, diamond or the
diamond-containing material may be treated with direct current (DC)
plasma in a 100% hydrogen atmosphere of 1 Torr for 15 to 30
minutes. Silicon carbide and aluminum nitride may also be kept in a
vacuum at 1600.degree. C. and 1200.degree. C., respectively, for
about 60 minutes to provide the cilia.
[0056] The semiconductor device 1 of this embodiment is included in
a ball grid array (BGA) package, which has a face-down structure.
This package is, for example, mounted on a mounting board such as a
multilayer printed circuit board. The semiconductor device 1 with
the heat spreader 2 of this embodiment allows a low-resistance,
high-density signal wiring and a low-cost, high heat-dissipation
package, thus improving the reliability of mounting of the
semiconductor device 1 and bonding of the metal heat sink 4 or the
metal radiating fin 5.
[0057] FIG. 5A is a sectional view of a heat spreader according to
a fifth embodiment of the present invention. This heat spreader
includes a diamond layer 110, polymer adhesive layers 111 provided
on the top and bottom surfaces of the diamond layer 110, and metal
or ceramic members 112 bonded on the polymer adhesive layers 111.
FIG. 5B shows a heat spreader according to a modification of this
embodiment. In this heat spreader, one polymer adhesive layer 111
and one metal or ceramic member 112 are provided on one surface of
the diamond layer 110.
[0058] This diamond layer 110 is composed of a polycrystal having a
fiber structure across the thickness. The diamond layer 110 can be
formed by controlling the conditions of nucleation and deposition
by chemical vapor deposition (CVD). The diamond layer 110 has a
thickness of, for example, 20 to 100 .mu.m.
[0059] An example of methods for forming this diamond layer 110
will now be described. To control the nucleation density, a surface
of a substrate (such as a silicon substrate) on which diamond is to
be deposited is polished with a diamond powder having an average
particle diameter of about 15 to 30 .mu.m. Alternatively, the
surface of the substrate is dipped in liquid alcohol containing the
same diamond powder to apply supersonic vibration to this liquid
for 5 to 15 minutes. After being washed to remove the diamond
powder adhered to the surface, this substrate is introduced into
diamond deposition equipment. The reactor of this equipment is
evacuated and provided with a mixture of hydrogen gas and 3%
methane gas to maintain a pressure of 90 Torr in the reactor. Then,
microwave plasmas are generated in the reactor while the substrate
is kept at 870.degree. C. to 950.degree. C. By this method,
deposition was performed for 5 hours to provide a diamond layer
having a diameter of 50 .mu.m. Observation of a cross section of
this diamond layer by electron microscopy demonstrated that the
diamond layer had a fiber structure across the thickness.
[0060] The diamond layer 110 has a thermal conductivity of 500
W/(m.multidot.K) or more across the plane and thickness. The
bonding surfaces of the diamond layer 110 and the metal or ceramic
member 112 have a thermal conductivity of 4.times.10.sup.6
W/(m.sup.2.multidot.K) or more.
[0061] The diamond layer 110 has a higher thermal conductivity
across the plane and thickness than any other material at present
used for heat spreaders. This diamond layer 110 can have a thermal
conductivity of 500 W/(m.multidot.K) or more, irrespective of its
crystalline structure. Among various diamond layers, ones having a
fiber structure across the thickness, as in this embodiment, are
more preferable because such diamond layers provide low grain
boundary density to prevent an increase in thermal resistance, thus
increasing the thermal conductivity by 50.+-.25%.
[0062] These diamond layers serve excellently as the main component
of a heat spreader for semiconductor packages from the viewpoints
of thermal conductivity, thermal stress during bonding, and
air-tightness. In addition, the diamond layers have a sufficient
strength and flatness. If, for example, one metal or ceramic member
112 is bonded on only one surface of the diamond layer 110, as in
FIG. 5B, the diamond layer 110 may be supposed to warp the heat
spreader due to stress concentration at one surface and, in many
cases, cause cracking during or after bonding. However, diamond has
high mechanical strength, which prevents warpage and cracking in
the heat spreader. These diamond layers preferably have a thickness
of at least 20 .mu.m, more preferably at least 50 .mu.m, for
securing the strength. On the other hand, thicknesses over 100
.mu.m undesirably produce such an excessive mechanical strength as
to make it difficult to process the diamond layer, and increase the
manufacturing cost.
[0063] As shown in FIG. 5A, the top and bottom surfaces of the
diamond layer 110 may be bonded with the metal or ceramic members
112, which may be made of the same material or materials having
nearly equivalent thermal expansion coefficients. Such metal or
ceramic members 112 can generate nearly equivalent thermal stresses
at both surfaces of the diamond layer 110 to minimize the warpage
of the heat spreader. The members 112 are preferably made of the
same material and bonded on the top and bottom surfaces of the
diamond layer 110 at the same time.
[0064] The polymer adhesive layers 111 for bonding the members 112
to the diamond layer 110 are made of an organic polymer adhesive
such as general epoxy resins, phenol resins, or their mixtures.
These polymer adhesive layers Ill may contain a powder of a high
thermal conductivity metal such as silver, copper, and aluminum. In
addition, the polymer adhesive layers 111 may also be made of an
inorganic polymer adhesive.
[0065] A preferable bonding method will now be described. A surface
of the member 112 is uniformly coated with a polymer adhesive
having a thickness of 5 to 50 .mu.m, which is dried if containing a
solvent. The adhesive surface of the member 112 is overlapped with
the diamond layer 110. The polymer adhesive is then polymerized and
cured by hot pressing at about 70.degree. C. to 150.degree. C. In
this method, more preferably, the polymer adhesive applied on the
member 112 is mildly preheated to polymerize the polymer adhesive
slightly for use in the state of a solid film at room
temperature.
[0066] Such a polymer adhesive layer 111 generally has poor
thermal-conductivity. This polymer adhesive layer 111, if having a
large thickness, decreases-the total thermal conductivity of the
heat spreader. Therefore, the polymer adhesive layer 111 preferably
has a thickness of 5 .mu.m or less, more preferably, 3 .mu.m or
less. The polymer adhesive, before cured, spreads over micropores
on the surface of the diamond layer 110, thus providing a highly
adhesive, extremely thin polymer adhesive layer.
[0067] The members 112 are formed by molding a high thermal
conductivity metal with good adhesion, such as silver, copper,
aluminum, their alloys, aluminum nitride, and silicon carbide,
into, for example, a foil, a plate, or a radiating fin.
[0068] FIG. 6A is a sectional view of a heat spreader according to
a sixth embodiment of the present invention. In this heat spreader,
the members 112 are bonded on the top and bottom surfaces of the
diamond layer 110 with the polymer adhesive layers 111. FIG. 6B is
a sectional view of a heat spreader according to a modification of
this embodiment. In this heat spreader, one member 112 is provided
on one surface of the diamond layer 110 with the polymer adhesive
layer 111. These heat spreaders are characterized by ciliary
diamond layers 113. That is, cilia are formed on one or both
bonding surfaces of the diamond layer 110 in this embodiment.
[0069] The ciliary diamond layers 113 can be formed by treating one
or both surfaces of the diamond layer 110 with DC plasma in a
hydrogen atmosphere. The ciliary diamond layers 113 may also be
formed on fibrous or microcrystalline diamond layers, which will be
described below. The cilia typically have end diameters of several
to tens of nanometers and lengths of several to hundreds of
micrometers.
[0070] The polymer adhesive spreads over the cilia to form a thin,
adhesive polymer adhesive layer, thus providing especially
desirable adhesion. In addition, even if the members 112 are made
of materials having different thermal expansion coefficients, the
ciliary diamond layers 113 can reduce the thermal stress. The
ciliary diamond layers 113 preferably have a thickness of 0.2 to 3
.mu.m. An excessively small thickness cannot provide high adhesion
for the ciliary diamond layers 113. On the other hand, an
excessively large thickness increases the cost for the ciliary
diamond layers 113 and decreases the mechanical strength of the
ciliary diamond layers 113 to result in a peeling bonding surface.
The other characteristics and conditions such as film thickness are
the same as in FIGS. 5A and 5B.
[0071] FIG. 7A is a sectional view of a heat spreader according to
a seventh embodiment of the present invention. FIG. 7B is a
sectional view of a heat spreader according to a modification of
this embodiment. These heat spreaders use a diamond layer 114
having a microcrystalline structure instead of the diamond layer
110 having a fiber structure as shown in FIGS. 5A, 5B, 6A, and 6B.
In the heat spreader in FIG. 7A, the members 112 are bonded on the
top and bottom surfaces of the diamond layer 114. On the other
hand, in the heat spreader in FIG. 7B, one member 112 is bonded on
one surface of the diamond layer 114. Such a microcrystalline
diamond layer 114 can also provide a thermal conductivity of 500
W/(m.multidot.K) or more because diamond has a high thermal
conductivity. In addition, the microcrystalline diamond layer 114
can reduce the thermal stress and secure such flatness that the
diamond layer 114 can be easily bonded to a semiconductor device or
package. Therefore, the microcrystalline diamond layer 114 is as
effective as the ciliary diamond layers 113.
[0072] An example of methods for depositing the microcrystalline
diamond layer 114 will now be described. To control the nucleation
density, a diamond powder having an average particle diameter of
about 5 nm is applied on a surface of a substrate on which diamond
is to be deposited. This substrate is dried, and then introduced
into diamond deposition equipment. The reactor of this equipment is
evacuated and provided with a mixture of hydrogen gas and 5% to 10%
methane gas to maintain a pressure of 100 Torr in the reactor.
Then, microwave plasmas are generated in the reactor while the
substrate is kept at 800.degree. C. or less. By this method,
deposition was performed for 5 hours to form a microcrystalline
diamond layer having a diameter of 80 .mu.m.
[0073] The polymer adhesive layers 111 are not necessarily used in
the fifth to seventh embodiments.
[0074] The diamond layers 110 and 114 in FIGS. 5A, 5B, 6A, 6B, 7A,
and 7B are separated from substrates. These diamond layers 110 and
114 may be separated by a known method. On the other hand, the
diamond layers 110 and 114 are not necessarily separated from the
substrates. In this case, only one metal or ceramic member 112 may
be bonded on a surface of the diamond layers 110 and 114 facing
away from the substrates. In addition, another metal or ceramic
member 112 may be bonded on a surface of the substrates facing away
from the diamond layers 110 and 114.
EXAMPLES
[0075] Examples of the present invention will now be described.
Example 1
[0076] A diamond layer having a thermal conductivity of 800
W/(m.multidot.K) or more was formed on the reverse surface of a
silicon wafer by CVD. This diamond layer, which was a microcrystal
having a thickness of 0.05 mm, was notched in advance to make the
diamond layer discontinuous. These notches suppress warpage of the
wafer and facilitate division of the wafer into chips. Then,
semiconductor devices were prepared on a surface of the silicon
wafer facing away from the diamond layer. Semiconductor chips with
a diamond heat spreader were prepared from this silicon wafer.
These chips had an external size of 23 mm by 25 mm and a power
consumption of 70 W.
Example 2
[0077] Resin wiring substrates were prepared with a liquid crystal
polymer as a base resin. The resin wiring substrates each had
copper foils thermally compressed on both surfaces. One of these
copper foils was etched to form a wiring layer having a pattern,
and was then coated with an insulating resin. The semiconductor
chips prepared in Example 1 were mounted on the resin wiring
substrates by wire bonding to form semiconductor packages having a
face-down structure. The semiconductor chips each had 478 pins in
the semiconductor packages.
[0078] The semiconductor chips in the present invention are not
limited to ball grid array (BGA) packages and may be applied to
various packages.
Example 3
[0079] Ten samples were selected from the semiconductor packages
prepared in Example 2. Each heat spreader in these samples was
partially coated with aluminum having a thickness of 100 nm to
equip the heat spreader with an aluminum radiating fin having an
external size of 35 mm by 39 mm. On the other hand, ten additional
samples were selected from the semiconductor packages prepared in
Example 2. Each heat spreader in these samples was coated with a
polymer adhesive on its ciliary surface to equip the heat spreader
with the aluminum radiating fin. A heat cycle test was performed on
both samples. This test was continued for 500 cycles of -40.degree.
C., room temperature, and 110.degree. C. This test showed that the
heat spreaders in both samples did not develop cracks or other
defects.
Example 4
[0080] By the above-described method for depositing a fibrous
diamond layer, a diamond layer having a thickness of 50 .mu.m was
deposited on a silicon chip of 30 mm by 30 mm. Observation of a
cross section of this diamond layer by electron microscopy showed
that columnar (fibrous) crystals having a diameter of 2 to 15 .mu.m
grew across the thickness. Another observation showed that a
diamond layer prepared by the method for depositing a
microcrystalline diamond layer had a microcrystalline structure.
Measurements by laser flashing showed that the fibrous diamond
layer and the microcrystalline diamond layer have thicknesses of
1500 W/(m.multidot.K) or more and 900 W/(m.multidot.K) or more,
respectively.
[0081] Next, an epoxy adhesive having a thickness of about 25 .mu.m
was uniformly applied on a surface of a copper foil having a
thickness of 50 .mu.m. The adhesive surface of the copper foil was
bonded to a surface of the fibrous diamond layer, which was
subjected to a pressure of 50 kg/cm.sup.2 by hot pressing at
150.degree. C. for 15 minutes to cure the adhesive, providing a
heat spreader of 30 mm by 30 mm. Through this process, a total of
ten heat spreaders were prepared. A heat cycle test (100 cycles of
-60.degree. C. to 200.degree. C.) was performed on these heat
spreaders, and demonstrated that defects such as peeling and
cracking did not occur.
Example 5
[0082] The fibrous diamond layers prepared in Example 4 were
treated with DC plasma in a 100% hydrogen atmosphere of 1 Torr for
15 minutes. The resultant diamond layers had a ciliary surface, as
shown in an electron micrograph in FIG. 9. As in Example 4, these
diamond layers were bonded to copper foils having a thickness of
100 .mu.m, single-crystal silicon substrates, and alumina
substrates, none of which caused defects such as peeling and
cracking after a thermal shock test and a cycle test.
* * * * *